Hello again:
geots wrote:Jesus, I realize that a 5 game margin (and I am making these figures up) after 20 games will represent a much much bigger elo difference than a 5 game margin after 300 games.
But what surprised me is if an engine leads by 13 games after 360 games, and in the next 62 games he increases the lead by 7 more games- to lead at 422 games by a total of 20 games- I would have thought that increasing the lead by 7 games the elo difference would have had to increase by at least 1 elo point. But it doesn't. It is +14 either way. There is no argument there for me to make- it either does or it doesn't. It just sort of surprises me- that's all. (Of course it wouldn't when you are up around 5000 games or something like that. Then 30 more wins wouldn't affect it.) But I thought it would make at least 1 elo point difference at 350 or 400 games. Oh well. No big deal.
george
For the first 360 games, I get a rating difference of ~ 12.55 Elo, not 14 Elo; if I am not wrong, a lead of 20 games after 422 games means a rating difference of 400·log(221/201) ~ 16.48 Elo, so there is a difference of 400·[log(221/201) - log(186.5/173.5)] ~ 3.93 Elo more less.
As you well know, rating difference is computed by the formula 400·log(points_A/points_B), where points_A and points_B are the number of points of engines A and B. Of course: points_A + points_B = n = number of games of the match.
I tried to put this rating difference in terms of (wins - loses)... I thought that I will not reach anything useful, but I achieve it, at last. It is indeed very easy:
Code: Select all
n = wins + loses + draws = w + l + d; d = n - w - l
(Rating difference) = rd = 400·log[(w + d/2)/(l + d/2)] = 400·log[(2w + d)/(2l + d)] = 400·log{[2w + (n - w - l)]/[2l + (n - w - l)]} = 400·log{[n + (w - l)]/[n - (w - l)]}
(Rating difference) = rd = 400·log{[n + (w - l)]/[n - (w - l)]}
So, in your first case (from Houdini POV), where n = 360 and (wins - loses) = 13, rd = 400·log[(360 + 13)/(360 - 13)] ~ 12.55 Elo, as I said before; when n = 422 and (wins - loses) = 20, then rd = 400·log[(422 + 20)/(422 - 20)] ~ 16.48 Elo (from Houdini POV), as I already wrote.
I think that you wrongly got those +14 Elo for Houdini due to roundings: when 360 games were played, the result was 186.5 - 173.5 in favour of Houdini, which is around 51.81% - 48.19% (which leads to ~ 12.55 Elo difference), but you rounded up to 52% - 48%, getting ~ 13.9 ~ 14 Elo difference. The same applies when 422 games are played: a 20-game lead means a provisional result of 221 - 201 (in favour of Houdini), which is more less 52.37% - 47.63% (so, around 16.48 Elo difference), instead of your same rounding of 52% - 48%, getting again ~ 13.9 ~ 14 Elo difference. Please correct me if my guesses are wrong.
Summarizing: if you are going to compute rating difference manually, I recommend you to do it with the number of points of each engine instead of the relative scores (I mean, the percentages): you will avoid nasty roundings that hurt the calculation. Please do not hesitate in asking doubts if you have them.
Regards from Spain.
Ajedrecista.